Research On Multicast Congestion Control

With the evolvement of Internet based on TCP/IP, the scale, users and traffics of it have experienced an explosive growth since 1990'5. Then network congestion has become more serious and complex due to the ever-increasing network application types and dynamic network Parameters such as active sessions and round trip time. Congestion often results in decline of quality of service(QoS) in terms of transmission delay and throughput, while the network resource utilization like bandwidth and buffers are also affected seriously. The congestion control is always a hot spot in the field of network research.Internet primarily relies on TCP end-to-end congestion control to avoid network congestion. But TCP strategies couldn't meet various demands of every application on the complex network. In fact, it will be more effective for detecting and preventing congestion if the routers perform queue management schemes. Congestion control strategies for the routers have been discussed widely. Multimedia applications such as video and audio have come forth continuously in recent years. UDP Protocol is employed to transfer multimedia flows. However, UDP flows are not friendly to TCP flows because they have no congestion control scheme, so it's necessary to develop congestion control schemes for UDP flows. These schemes must not only support certain QoS but also be TCP-Friendly.This paper begins with the basic concept of IP multicast and focuses on the principal problems such as TCP-Friendly, scalability, fairness; then we describe the lastest researches and developments on mulcicast congestion algorithms, classify them from different aspects and different algorithms are analyzed and compared; furthermore introduce the layered multicast and layered coding techniques of video stream.By comparing the merits and faults of DiffServ and IntServ, it expounded the function module of DiffServ and traced the process. It analyzed the advantage and problems while combining IP multicast with DiffServ.Systematic research to meet practical requirements of IP based networks is performed in depth. The primary works and innovations of this paper include but not limited to:(1) Effective multicast congestion control mechanism is urgently needed with the deployment of multimedia applications in Internet, based on the analysis results of the present layered multicast, a TCP-Friendly active layered multicast congestion control mechanism with rapid self-adaptive at receivers called ALMCC is proposed. It uses active label layered and adapts to the bandwidth of network rapidly at receivers according to the packet delay. Simulation results show that ALMCC enhances the performances of layered multicast congestion control and characterizes with more responsive, lower loss rate and better TCP-Friendliness.(2) Network heterogeneous problems is more outstanding with the development of multimedia applications in Internet, and it calls for new demand for traditional multicast congestion control, layered multicast is considered to be an efficient approach to cope with the network heterogeneity. To conquer the problems of quality instability, control complexity, and frequent changes of multicast tree in traditional layered multicast, a layered multicast congestion control mechanism base on DiffServ called LMCC is proposed. It marks and forwards the packets on the premise of the fairness reserving of bandwidth, so it adapts the heterogeneous network well. Simulation results show that LMCC characterizes with more responsive, more stable, better TCP-Friendliness and low loss rate.For the multicast congestion control is such a complicated problem, this paper just researches some points of it. To resolve the congestion problem completely and successfully, you should integrate more tactics to control it through various parts and angle of network.